Target seeking by missile interceptors can be done several ways. The most common approach uses ground-based radar for coarse guidance, then an infrared (IR) seeker for terminal guidance. IR seekers come in two varieties: passive and active. Passive sensors work with a two dimensional image and rely on the heat given off by the target for identification and tracking. This can be very effective but is subject to noise, clutter and countermeasures such as decoys. The second method uses a laser on the interceptor to scan the target. This method is very effective at shorter ranges but not suitable for acquiring targets at long distances or for scanning large volumes of space for initial target acquisition. The three dimensional (3-D) imaging capability and the single wavelength of active sensors makes them very effective for distinguishing targets from decoys and cutting through natural clutter and thermal noise. An ideal solution would be to have both systems onboard: passive for mid-range target acquisition and active laser for terminal guidance and defeat of noise, clutter and countermeasures. In the past this has not been achieved because of the cost and the limited space available, weight constraints and the limited power available in most interceptors to implement two separate systems. To date no effective technology is available to make a single focal plane array suitable for both passive and active IR seekers.
As illustrated in U.S. Pat. No. 5,300,780 multispectral image analysis is used to separate a missile or target reentry vehicle from background. The multispectral performance is obtained by mounting filters on a color wheel in front of a focal plane array.
Note that a two color infrared focal plane array for multiple IR bands is described in U.S. Pat. No. 4,956,686 in which infrared detectors of two sensitivity types are shown.
Also known are various ways of making infrared HgCdTe arrays such as described in U.S. Pat. Nos. 5,318,666; 5,599,733; and 6,180,945. U.S. Pat. No. 6,329,649 describes the combination of linear and two-dimensional arrays of IR sensors along with an associated silicon readout integrated circuit (ROIC) substrate for the array.
U.S. Patents describing methods of making radiation detecting arrays include U.S. Pat. Nos. 4,527,183; 4,290,844; 4,595,428; 4,597,002 and 5,300,786.
Finally U.S. Pat. No. 5,960,097 describes a missile and tracking system operating on data samples from a focal plane array of an electro-optical sensor.
Note that the above multispectral systems do not envision using a single monolithic device to passively detect both IR and returned laser pulses from a LADAR device.